This invention relates to an improved apparatus for gripping a down hole tubular for rotation that it is suitable for use in a drilling machine, such as an oil well drilling machine, and that operates simply and reliably, with a minimum of parts.
It has been recognized for some time that there is a need for tools to engage down hole tubulars such as drill pipes and casings in a high speed manner for rotation in a drilling machine. Depending upon the size of the down hole tubular the apparatus can be designed either to fit around the upper end of the tubular as described in U.S. patent application Ser. No. 07/107,268 (parent application of U.S. Pat. No. 4,867,236) now abandoned, assigned to the assignee of the present invention. Alternately, the engaging apparatus can be designed to fit into the upper end of the down hole tubular and to grip the tubular from within, as described in U.S. Pat. No. 4,762,187, also assigned to the assignee of the present invention.
Both of these devices utilize friction brakes to move the clamping jaws into and out of engagement with the down hole tubular. Though this approach has been found effective and reliable, it is not without disadvantages. In particular, the braking mechanisms result in relatively complex linkages with a relatively large number of parts. There can be a concern among some users that parts may become disengaged from the mechanism and fall into the borehole, thereby creating significant problems. Also, in some applications the device itself moves axially with respect to the remaining portions of the drilling machine. Such axial movement may complicate the braking mechanism used to engage and disengage the clamping elements from the down hole tubular.
The present invention is directed to improved devices for engaging a down hole tubular for rotation, which to a large extent overcome the disadvantages discussed above by completely eliminating the need for a friction brake system.